Screen Basket Optimized For Removal Of Stickies From Adhesives-Contaminated Recyclable Fiber

ABSTRACT

A screen structure which is unusually effective at removing stickies from recyclable fiber but is tolerant of substantial swings in throughput which result in variations in the flow velocity through the screen-slot velocity. One example of the screen structure is created by forming a very large number of similarly shaped vanes then locking them into a ring structure to form a cylindrical screen basket but equivalent surface configurations can also be formed into sheet stock.

CLAIM FOR PRIORITY

This non-provisional application is based upon U.S. Provisional PatentApplication No. 61/461,117, of the same title, filed Jan. 13, 2011. Thepriority of U.S. Provisional Patent Application No. 61/461,117 is herebyclaimed and the disclosure thereof is incorporated into this applicationby reference.

TECHNICAL FIELD

Recycling is fast becoming essential for almost every recyclablecommodity, yet differences between prices for commodities obtained fromnature and those obtained from waste often do not economically justifyuse of recyclable materials. In the case of fiber obtained from recyclestreams of waste paper, it is often quite difficult to render the fiberequivalent in quality to fiber obtained from virgin pulp withoutincurring costs exceeding the price differential between virgin fiberand the recyclable fiber contained in readily available waste streams.

BACKGROUND

Achieving virgin equivalent quality from recycled paper is increasinglydifficult as fiber from lower and lower grade sources is used. Curbsiderecycled paper is usually considered just about the lowest possiblegrade of paper being recycled today. One factor which seems tocontribute to the difficulty of obtaining fiber having qualityequivalent to virgin fiber from curbside recycled paper is the presenceof large amounts of “stickies” and other contaminants in the paper; butindustrial/commercial waste papers are also becoming increasinglycontaminated, especially with troublesome adhesives. Stickies commonlyresult from pressure sensitive labels in the waste paper but can becreated by other adhesives, plastic window envelopes and the like.During the papermaking process, stickies in the furnish cause problemsboth by precipitating out of the furnish onto machine parts as well asby remaining in the web where they contribute to dense spots ofadhesive, ink, plastic, fiber and a host of other contaminants. Stickiesare especially problematic when recycle fiber is being used for tissueproducts as, in bath and facial tissue, each ply of tissue may only havea thickness equivalent to perhaps seven to ten layers of fiber, so thedark dense spot resulting from a stickie which finds its way into thefinished sheet detracts both from the aesthetic appearance of the sheetand its functional integrity. Stickies that deposit out on machineclothing interfere with the proper movement of water and/or air throughthe fabric, again potentially contributing to defects in the finishedproduct.

As waste paper is converted into pulp which is usable in making tissueand towel products, it is subjected to many of the same processes usedwith virgin pulp. In fact many mills will use a combination of virginand recycle pulp to “dial-in” quality. This can lead to difficulties infiber processing as many of these procedures are relatively sensitive tothroughput variations. An especially important process is “screening” inwhich pulp is fed through a “screen” to remove dirt and othercontaminants. Virtually all of the pulp fed to a papermachine will passthrough a series of screens, each configured to remove contaminantsprogressively smaller in size than the screen before. Each screen willtypically also have some means for removing contaminants lodged on thescreen so that the screen does not become blocked. The term “screen” isoften used both to refer to the overall apparatus used for removingimpurities from pulp and for the actual perforate structure which formsthe heart of that apparatus. In this application, the aggregate of thosestructures that form the removable perforate structure are typicallyreferred to as the screen basket. This application relates to theperforate screen structure and more particularly to the shape of thesurface of the screen structure which contacts the fiber suspension fromwhich impurities are to be removed. Typically, foils moving relative tothe screen basket are used for this purpose. These foils arehypothesized to induce negative pressure pulses that clear debris off ofthe screen basket so that it can pass out of the screen through a rejectline.

SUMMARY OF THE INVENTION

This invention relates to a screen structure which is unusuallyeffective at removing stickies from recyclable fiber but is tolerant ofsubstantial swings in throughput which result in variations in the flowvelocity through the screen-slot velocity.

In modern screens, a great deal of attention is paid both to thehydrodynamics of the flow system as it passes over the screen structurebut also to the stresses imposed on the screen as it is subjected toalternating pressure pulses which temporarily induce backflow throughthe openings in the screen which ideally remove debris which mightotherwise occlude the screen and thereby reduce the screening systemscapacity. There are two primary techniques used for constructingscreens. In the first, a web structure, typically a sheet of stainlesssteel, has a variety of inter-cooperating grooves, channels,perforations and slits formed in both of its surfaces. The sheet is thenrolled into a cylindrical shape and incorporated into the screen system.In the second, a plurality of vanes are formed, often each vane willhave a quite complex shape possibly including tapers, grooves, lands,relieved regions and dressed away areas so that when the vanes areassembled into a cylindrical array, precisely shaped slits are formedthrough the resulting cylindrical shell formed by the multitude ofvanes.

There are advantages to each method of construction; but, in screensformed by either technique, the goal is to precisely form a surfacejoined to slits in parallel in which the flow of water will efficientlyconduct fibers through the slits while rejecting contaminants withoutoccluding the surface of the screen. The present invention is thought tobe most easily practiced by forming a very large number of similarlyshaped vanes then locking them into a ring structure to form acylindrical screen basket but equivalent surface configurations can alsobe formed into sheet stock although the manufacturing cost may be higherdue to the difficulties involved in forming precise slits, channels,grooves and contours in the required size.

While large stickies are especially problematic when they find their wayinto the sheet and the effect of very small stickies in the sheet itselfcan be difficult to detect, it is not sufficient to remove only thelarger stickies at the screens as the adhesives, particularly thepressure sensitive adhesives, tend to aggregate during the papermakingprocess and grow into larger stickies. Accordingly, one common way ofmeasuring the effectiveness of screening is to separately measure thetotal area of stickies removed in several size ranges. We prefer toanalyze stickies contents in terms of the stickies content by total areain the ranges of 0.001-0.04 mm², 0.04-0.3 mm² and over 0.3 mm². Inaddition, it is sometimes useful to aggregate the 0.04 to 0.3 mm² andover 0.3 mm² ranges into a single category of over 0.04 mm². Typically,most well designed screens are reasonably effective for stickies over˜0.3 mm² in area but will have more difficulty with stickies in the twosmaller ranges of 0.001-0.04 mm² and 0.04-0.3 mm². Further, it isgenerally thought that there is a tradeoff between designing screens tobe effective on the smaller size ranges of stickies and the amount offiber that can be effectively cleaned by that screen in a given period.We have found that the screens of the present invention have surprisingeffectiveness with smaller stickies removal coupled with the ability toprocess large quantities of fiber over a wide range of slot velocities.It is considered quite surprising that these screens could combine theability to both remove large fractions of the smaller stickies andprocess large amounts of fiber over a wide range of slot velocities.Effective removal of large stickies is, however, the sine qua non ofscreen design. A screen design which is not extremely effective inremoving large stickies can only be employed in special circumstances.

We have found that surprisingly effective removal of stickies fromrecyclable waste can be achieved by passing pulp derived fromindustrial, commercial and post-consumer waste through a metallic screenbasket having an accepts contacting surface approximating that of aright circular cylinder having an axis “A”, a circumference “C” and adiameter “D”, said surface comprising a plurality of sequences offacets, each sequence comprising a generally circumferentially extendingfacet, an upstream generally diametrally extending facet adjacentthereto, and a downstream generally diametrally extending facet adjacentthereto, each said generally circumferential facet being generallyparallel to the axis “A” of the cylinder and having a leading edge and atrailing edge, each said leading edge and trailing edge as well as eachsaid upstream generally diametrally extending facet and each saiddownstream generally diametrally extending facet being generallyparallel to the axis “A” of the cylinder, each said leading edge beinglocated upon a cylindrical surface S₁, and each said trailing edge beinglocated upon a cylindrical surface S₂, the diametral difference “δ”between the distance from the axis “A” of the cylindrical surface S₁from the diametral distance from the axis “A” of the cylindrical surfaceS₂ being between about 0.4 mm to about 0.6 mm, the normal direction tothe surface of each said generally circumferential facet in eachsequence of facets having a component directed toward the adjacenttrailing edge of an adjacent generally circumferential facet in anadjacent sequence of facets , the angle “α” between the normal to eachsaid generally circumferential facet and the diametral direction of saidright circular cylinder being between about 80° and 76°, the distance“t” from the leading edge to the trailing edge of each said generallycircumferential facet being between about 2.3 mm and 2.5 mm, theupstream generally diametrally extending facet of each sequenceadjoining the leading edge of a generally circumferential facet and thedownstream generally diametrally extending facet of each sequenceadjoining the trailing edge, the distance between the upstream generallydiametrally extending facet of each sequence and the downstreamgenerally diametrally extending facet of the next adjacent sequence “w”being between about 0.11 and 0.14 mm, a relieved channel leading fromthe accepts side to the rejects side of said screen being definedbetween the upstream generally diametrally extending facet of eachsequence and the downstream generally diametrally extending facet of thenext adjacent sequence.

In some embodiments, the screen basket is formed from at least oneunitary metallic sheet, usually of stainless steel, each sheet having aplurality of trenches formed into its surfaces and a plurality of slitsformed therethrough.

In other embodiments, a corrosion resistant hardened surface is disposedupon said screen basket; preferably said corrosion resistant hardenedsurface comprises a major proportion of chromium having hardness of atleast about 65 on the Rockwell C scale in a thickness of at least 0.2mils up to about 1.0 mils.

Still yet other features and advantages of the invention will becomeapparent from the following description and appended Figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in detail below with reference to thedrawings wherein like numerals designate similar parts and wherein:

FIG. 1 is a partially cut away perspective of a known construction of ascreen basket which is suitable to be adapted for practice of thepresent invention by replacement of the vanes therein by vanes havingthe configuration described herein.

FIG. 2 is a schematic illustration of the geometry of the supply side ofa screen basket constructed from a large number of vanes.

FIG. 3 is a schematic illustration of a foil in relation to severalvanes of a screen basket.

FIG. 4 is a schematic illustration of the theorized flow pattern in theneighborhood of the slits in a screen basket of the present invention.

FIG. 5 illustrates the distribution of stickies by size in the supplystreams used in experiments conducted to determine the effectiveness ofseveral screen baskets.

FIG. 6 illustrates the distribution of stickies by size in the acceptsstreams obtained in experiments conducted to determine the effectivenessof several screen baskets.

FIG. 7 illustrates the Average Cleanliness Efficiencies obtained for thevarious size ranges of stickies obtained in experiments conducted todetermine the effectiveness of several screen baskets.

FIG. 8 illustrates the relationship between the Average CleanlinessEfficiencies obtained for the various size ranges of stickies and theslot widths of the screens used in experiments conducted to determinethe effectiveness of several screen baskets.

FIG. 9 illustrates the relationship between the Average CleanlinessEfficiencies obtained for the various size ranges of stickies and theprofile heights of the screens used in experiments conducted todetermine the effectiveness of several screen baskets.

FIG. 10 illustrates the relationship between the Overall AverageCleanliness Efficiencies obtained and the slot width of the screens usedin experiments conducted to determine the effectiveness of severalscreen baskets.

FIG. 11 illustrates the correlation obtained between the Overall AverageCleanliness Efficiencies and the slot widths and profile heights of thescreens used in experiments conducted to determine the effectiveness ofseveral screen baskets.

FIG. 12 sets forth both the Area % of total stickies removed and thetotal mass flow of the accepts streams for each of the screens evaluatedwith profile height being indicated for each data point.

FIG. 13 sets forth both the Area % of total stickies removed and thetotal mass flow of the accepts streams for each of the screens evaluatedwith accepts tonnage being indicated for each data point.

FIG. 14 sets forth the Area % of total stickies removed in the sizerange of 0.001 to 0.04 mm² on a grid of the slot width and profileheight for each of the screens evaluated.

FIG. 15 sets forth the Area % of total stickies removed in the sizerange of 0.04 to 0.3 mm² on a grid of the slot width and profile heightfor each of the screens evaluated.

FIG. 16 sets forth the Area % of total stickies removed in the sizerange of greater than 0.04 mm² on a grid of the slot width and profileheight for each of the screens evaluated.

FIG. 17 sets forth the Area % of total stickies removed in the sizerange of greater than 0.3 mm² on a grid of the slot width and profileheight for each of the screens evaluated.

FIG. 18 illustrates the wide variations in Cleanliness Efficienciesresulting for each of the several size ranges of stickies as slotvelocity was varied for a screen basket with 0.19 mm slots and a profileheight of 0.6 mm.

FIG. 19 illustrates the significant reductions in the variations inCleanliness Efficiencies resulting for each of the several size rangesof stickies as slot velocity was varied for a screen basket with 0.14 mmslots and a profile height of 0.51 mm.

FIGS. 20-24 illustrate the performance of a variety of screen designs onvarious size ranges of stickies as slot velocity is varied.

DETAILED DESCRIPTION

The invention is described below with reference to a preferredembodiment. Such discussion is for purposes of illustration only.Modifications to particular examples within the spirit and scope of thepresent invention, set forth in the appended claims, will be readilyapparent to one of skill in the art.

Terminology used herein is given its ordinary meaning unless otherwiseindicated.

FIG. 1 illustrates a screen basket 30 comprised of a very large numberof longitudinally extending vanes 32 defining longitudinally extendingslits 34 therebetween, vanes 32 being held between flanges 36 joined bylongitudinally extending rods 38. Vanes 32 are reinforced bycircumferential ribs 40. This overall method of construction is knownfrom U.S. Pat. No. RE 38,738 E and is well suited to receive and retainvanes 32 as described herein.

FIG. 2 (with periodic reference to FIGS. 1 and 3) illustrates thecross-section of several vanes 32 of the present invention. Each vane 32has three facets: downstream generally diametrally extending facet 42,generally circumferentially extending facet 44 and upstream generallydiametrally extending facet 46. Upstream generally diametrally extendingfacet 46 adjoins generally circumferentially extending facet 44 atleading edge 48 while downstream generally diametrally extending facet42 adjoins generally circumferentially extending facet 44 at trailingedge 50 which preferably has a radius of curvature of about 0.6 mm. Oneach vane 32, centerline

extends toward geometrical axis “A” of screen basket 30. Leading edge 48of each vane 32 lies upon imaginary cylindrical surface S₁ while eachtrailing edge 50 lies upon imaginary cylindrical surface S₂, spaced adistance “6” of between 0.4 mm and 0.6 mm from imaginary cylindricalsurface S₁, this distance being referred to as the profile height. Eachgenerally circumferentially extending facet 44 has a thickness “t” ofbetween about 2.3 and 2.5 mm and is inclined toward the upstream at anangle “α” of between about 76° and 80° its respective diametrallyextending centerline

. Slit 52 having a width “w” of between about 0.11 mm and 0.145 mm isdefined between upstream generally diametrally extending facet 46 ofeach vane 32 and downstream generally diametrally extending facet 42 ofthe next vane upstream therefrom. Together the downstream generallydiametrally extending facet 42, trailing edge 50, generallycircumferentially extending facet 44 and upstream generally diametrallyextending facet 46 collectively define the supply contacting surface 54of screen basket 30.

FIG. 3 illustrates foil 56 having leading edge 58 and trailing edge 60defined thereupon. As leading edge 58 of foil 56 passes over each slit52, it is theorized that it introduces a negative pressure upon the slitit is passing over tending to clear the slit of stickies and otherdebris that may be deposited there, while the positive pressureresulting after trailing edge 60 of foil 56 passes over slit 52 tends todrag fiber therethrough while incidentally forcing stickies and otherdebris against rejects supply contacting surface 54 of screen basket 30(FIG. 1), there to remain until passage of a successive foil 56 inducesnegative pressure to dislodge stickies and debris. In conventionalpractice, the clearance between the supply contacting surface 54 andfoil 56 is a small fraction of an inch or just a few millimeters.

FIG. 4 illustrates the hypothetical formation of vortices 62 as flowpasses over trailing edge 50 of each vane 32. Some have theorized thatproper formation of vortices 62 helps to align fibers with slit 52easing the passage of longer fibers through slit 52. Others havehypothesized that proper formation of vortices ameliorates the formationof deposits between the slits of the screen.

Six different screen baskets having the general configurationillustrated in FIG. 1 were evaluated with recycled fiber samplescollected from industrial, commercial and post-consumer waste pulprecycling operations. The slot width and profile height for each of thescreen baskets, as reported by the manufacturers, are set forth inTable 1. Upon microscopic inspection, it was determined that thegeometry of the screen baskets varied considerably from that stated bythe manufacturer in several cases. Table 1 compares the Actual ScreenBasket Geometry to that reported by the manufacturers.

TABLE 1 Reported Screen Basket Actual Screen Basket SpecificationsGeometry Screen Basket Slot Profile Slot Profile Label Width, mm Height,mm Width, mm Height, mm A 0.10 0.9 0.11 0.90 V-1 0.11 0.7 0.11 0.70 V-20.12 0.5 0.13 0.50 V-3 0.15 0.7 0.16 0.67 V-4 0.15 0.7 0.14 0.51 V-50.15 0.7 0.19 0.62

Over a period of several months, the screen baskets were evaluated withpulp samples having average stickies contents and size variations as setforth in Table 2.

TABLE 2 Supply Stickies (per 100 OD g basis) 0.001-0.04 >0.040.04-0.3 >0.3 mm² mm² mm² mm² Count Area Count Area Count Area CountArea A 3,571 28.5 1,859 474.7 1,494 185.3 365 289.4 V-1 2,076 16.9 1,152305.6 936 117.3 216 188.3 V-2 4,674 40.0 2,830 739.2 2,262 282.1 568457.1 V-3 2,650 43.2 2,957 680.2 2,448 305.5 509 374.7 V-4 3,805 30.61,997 473.2 1,672 208.2 325 265.0 V-5 5,090 20.5 1,355 381.5 1,064 135.5291 246.0

On a gross basis the results obtained are set forth in the two parts ofTable 3.

TABLE 3 (part 1) Supply Accepts Rejects Mass Flow Reject % % % % % % % %% (ODSTPD) Production Ratio TSS Ash Cons GPM TSS Ash Cons GPM TSS AshCons Accept Rejects Supply ODSTPD A 0.16 1.10 6.88 1.02 3,466 0.99 7.390.94 565 1.51 5.66 1.40 213 50 263 373 V-1 0.14 1.08 6.95 1.01 3,5271.01 7.42 0.94 494 1.41 5.67 1.33 214 42 256 366 V-2 0.20 1.17 7.41 1.093,536 1.10 7.58 1.02 704 1.51 5.98 1.42 235 64 299 393 V-3 0.14 1.055.82 0.99 3,665 1.00 6.07 0.94 512 1.49 4.64 1.42 220 46 266 386 V-40.14 1.09 7.29 1.01 3,716 1.03 7.45 0.95 520 1.45 6.06 1.36 230 45 275393 V-5 0.14 1.08 7.39 1.00 3,574 1.04 7.52 0.96 501 1.35 6.26 1.26 22441 265 375

TABLE 3 (part 2) Thickening Vol. Reject OD Reject Slot Vel. Factor Rate,% Rate, % m/s A 1.36 14.0 19.0 1.29 V-1 1.31 12.3 16.4 1.38 V-2 1.2916.6 21.5 1.52 V-3 1.42 12.3 17.3 1.58 V-4 1.33 12.3 16.5 1.60 V-5 1.2512.3 15.4 1.54

The accepts stream samples from the screen were evaluated for stickiescontent with average results as set forth in Table 4.

TABLE 4 Accepts Stickies (per 100 OD g basis) 0.001-0.04 >0.040.04-0.3 >0.3 mm² mm² mm² mm² Count Area Count Area Count Area CountArea A 1,973 16.7 969 123.7 927 105.2 42 18.5 V-1 1,388 10.2 493 59.1476 52.2 17 6.8 V-2 1,734 16.4 896 103.0 876 91.2 20 11.8 V-3 2,717 24.91,520 172.0 1,490 160.5 30 11.5 V-4 1,537 12.1 632 72.5 619 66.4 12 6.1V-5 1,595 13.0 854 120.6 801 98.1 54 22.5

From these results, cleanliness efficiencies were obtained on both anumber basis and an area basis as set forth in the three parts of Table5. These results are also presented graphically in FIGS. 5-10 while FIG.11 presents a correlation between slot width, profile height and averagecleanliness efficiency.

TABLE 5 (part 1) Cleanliness Efficiency (Area) Cleanliness Efficiency(Count) >0.04 0.04-0.3 >0.3 >0.04 0.04-0.3 >0.3 mm², % mm², % mm², %mm², % mm², % mm², % A 74.4 40 94 49.1 39 89 V-1 81.6 50 96 58.7 50 93V-2 85.1 59 97 66.8 59 96 V-3 75.0 49 97 49.7 41 94 V-4 84.6 67 98 68.263 96 V-5 68.5 28 91 37.7 25 83

TABLE 5 (part 2) Screen Capacity Stickies Cleanliness Slot Profile Tonsper day Tons per day Total area of Area % Efficiency (Area) Width,Height, in Accept in Supply Stickies Stickies Removal >0.040.04-0.3 >0.3 mm mm Stream Stream in Supply Efficiency mm², % mm², %mm², % A-1 0.11 0.90 213 263 688.6 61.7 74.4 40 94 V-1 0.11 0.70 214 256439.7 70.8 81.6 50 96 V-2 0.13 0.50 235 299 1061.3 79.0 85.1 59 97 V-30.16 0.67 220 266 1028.9 64.1 75 49 97 V-4 0.14 0.51 230 275 712.0 77.984.6 67 98 V-5 0.19 0.62 224 265 537.4 527 68.5 28 91

FIGS. 12-17 graphically present relationships between slot width,profile height and stickies removal with tonnage production being notedfor each case.

TABLE 5 (part 3) Stickies Screen Total area of Total area of Area %Stickies Slot Profile Stickies in Supply Stickies in Accepts RemovalEfficiency Width, mm Height, mm 0.001-0.04 mm² 0.001-0.04 mm² 0.001-0.04mm² A-1 0.11 0.90 28.5 16.7 41.4% V-1 0.11 0.70 16.9 10.2 39.6% V-2 0.130.50 40.0 16.4  59% V-3 0.16 0.67 43.2 24.9 42.4% V-4 0.14 0.51 30.612.1 60.5% V-5 0.19 0.62 20.5 13.0 36.6%

As the demand on the fiber processing lines typically varies from timeto time depending upon the paper machine needs, it is quite advantageousfor a screen design to be able to provide a relatively consistent outputover a range of throughputs. To demonstrate the ability of screendesigns of the present invention to handle variations in throughputs,during the series of trials above, the performance of the screen wasrecorded as the slot velocity was varied. The following tables (Tables6-11) record the Cleanliness Efficiencies of the several screen designsset forth over a range of slot velocities.

Example 1 (Comparative)

Table 6 describes the performance of a screen, not of the presentinvention, in the above-described evaluation. FIG. 18 sets forth thoseresults graphically. It can be appreciated that not only are theefficiencies rather low but that they vary widely as slot velocity isvaried, making it quite difficult to reliably control the input to thepapermaking process as demand for fiber is varied. (Throughout theExamples, where the last line of a table is separated from the linesabove it by a heavy horizontal line, the values in that last line areaverages of the figures above in that table.)

TABLE 6 Screen Basket V-5 - Slot Width 0.19 mm/Profile Height 0.62 mmCleanliness Efficiencies (%) Slot velocity Stickies Area Size Ranges(m/s) >0.04 mm² 0.04-0.3 mm² >0.3 mm² 1.28 67.3 33.3 91.7 1.27 69.5 35.395.4 1.28 68.7 5.2 95.1 1.29 75.5 24.1 93.9 1.28 74.6 40.0 90.2 1.2877.3 38.7 93.8 1.16 76.5 44.3 93.3 1.16 58.5 16.4 86.0 1.19 43.6 −5.082.7 1.20 69.1 27.7 91.5 1.20 65.0 25.6 82.8 1.20 51.9 31.2 65.7 1.1649.5 23.0 84.8 1.16 70.3 7.2 95.5 1.18 76.5 45.2 91.1 1.17 66.0 18.088.0 1.17 76.2 27.0 94.0 1.17 72.1 43.4 93.2 1.15 79.6 33.4 96.4 1.2258.9 29.3 80.6 1.16 72.0 −2.3 95.4 1.16 68.2 13.8 92.6 1.19 75.1 37.291.8 1.19 80.5 43.3 92.9 1.29 71.1 45.3 97.1 1.28 68.2 33.9 90.3 1.1562.1 8.9 92.9 1.16 56.0 16.7 87.0 1.23 47.9 4.3 81.2 1.22 52.5 7.4 87.21.19 68.6 48.7 90.8 1.20 52.1 32.5 79.9 1.22 79.3 56.0 93.3 1.22 79.045.7 96.6 1.28 83.8 23.5 98.4 1.29 75.2 44.9 89.5 1.16 62.3 7.8 96.21.16 86.0 42.9 98.3 1.18 78.0 57.4 92.7 1.17 74.0 19.8 95.3 1.32 78.339.3 95.1 1.33 69.1 46.2 93.9 1.34 66.7 23.9 91.5 1.35 59.5 9.7 88.91.22 68.5 28.4 90.8

Example 2

Table 7 sets forth results obtained with a screen which was found to beperforming exceptionally well for unknown reasons. Upon closeexamination, it was determined that not only did it not match thespecifications from the factory but it appeared that it had most likelyworn considerably from its initial configuration. As the slot width wasnarrower than manufacturer's specification, it was considered apparenthowever that not all of the variation could be due to wear. FIG. 19presents the results obtained with this screen graphically. It can beappreciated that the average efficiencies are not only very high but theresults remain quite consistent over a wide range of slot velocities.These results led the present inventors to determine whether theoutstanding and unexplained performance of this screen could beduplicated by manufacturing a screen with the same slot width andprofile height.

TABLE 7 Screen Basket V-4 - Slot Width 0.14 mm/Profile Height 0.51 mmCleanliness Efficiencies (%) Slot Velocity Stickies Area Size Ranges(m/s) >0.04 mm² 0.04-0.3 mm² >0.3 mm² 1.74 80.8 56.8 98.5 1.73 80.5 50.498.7 1.75 81.6 50.8 96.8 1.74 94.6 73.5 99.0 1.75 88.3 68.3 98.3 1.7590.9 75.7 95.3 1.58 93.8 83.2 100.0 1.58 85.6 70.1 99.0 1.61 89.5 76.496.3 1.61 92.6 78.4 99.5 1.60 81.3 42.7 99.4 1.63 82.9 63.4 100.0 1.5885.7 63.8 97.1 1.58 88.7 73.7 96.9 1.68 86.7 71.8 97.4 1.67 89.5 71.399.7 1.85 84.8 78.4 98.6 1.85 86.2 76.1 99.4 1.86 81.3 71.6 99.1 1.8681.8 66.6 97.0 1.67 87.1 69.3 100.0 1.67 82.2 65.2 99.4 1.67 78.9 67.797.6 1.67 83.5 73.3 95.7 2.04 83.6 68.9 97.1 2.04 50.0 30.0 79.8 2.0380.4 66.6 96.4 2.05 87.7 75.3 98.6 1.58 86.6 65.1 98.4 1.58 86.6 68.698.6 1.58 86.3 73.0 98.4 1.57 85.7 68.9 99.0 1.72 84.6 67.3 97.7

Example 3

Table 8 presents the results obtained with a screen of the presentinvention, V-2 which attempted to achieve the same slot width andprofile as found in screen V-4. The results obtained are presentedgraphically in FIG. 20. From these results, it can be appreciated thatscreen V-2 largely replicates the benefits of screen V-4.

TABLE 8 Screen Basket V-2 - Slot Width 0.13 mm/Profile Height 0.5 mmCleanliness Efficiencies (%) Slot Velocity Stickies Area Size Ranges(m/s) >0.04 mm² 0.04-0.3 mm² >0.3 mm² 1.34 88.3 65.6 98.6 1.35 84.1 65.599.4 1.38 75.5 35.1 98.9 1.44 80.2 36.0 100.0 1.35 88.7 57.9 98.7 1.3591.7 74.4 98.4 1.45 77.6 40.2 97.3 1.48 86.0 67.1 99.2 1.42 82.9 57.890.1 1.41 85.1 62.9 92.6 1.40 87.0 71.3 99.5 1.30 89.9 71.6 98.5 1.4488.0 61.6 98.8 1.45 91.0 65.8 100.0 1.44 78.5 46.4 95.2 1.55 88.8 73.797.9 1.35 89.6 62.3 98.1 1.35 79.5 54.4 92.0 1.40 85.1 59.4 97.4

Example 4 (Comparative)

Table 9 sets forth the results obtained with another screen V-1, not ofthe invention, while those results are presented graphically in FIG. 21.While the results are somewhat consistent with slot velocity, it can beappreciated from FIG. 21, that the efficiency of Screen V-1 is farinferior to screens of the present invention.

TABLE 9 Screen Basket V-1 - Slot Width 0.11 mm/Profile Height 0.7 mmCleanliness Efficiencies (%) Slot Velocity Stickies Area Size Ranges(m/s) >0.04 mm² 0.04-0.3 mm² >0.3 mm² 1.33 80.5 47.9 96.6 1.33 74.6 37.190.3 1.40 73.4 49.9 92.2 1.41 64.3 36.6 89.0 1.37 91.0 66.2 100.0 1.3873.8 45.9 96.0 1.41 85.5 55.4 97.1 1.41 84.1 55.0 96.1 1.47 88.7 62.596.9 1.47 88.5 52.8 100.0 1.33 92.5 59.5 100.0 1.33 78.7 30.1 98.8 1.3680.4 50.1 96.1 1.34 86.1 52.9 98.9 1.38 81.6 50.1 96.3

Example 5 (Comparative)

Table 10 presents the results obtained on another screen, V-3 not of theinvention, while those results are presented graphically in FIG. 22.While the results are somewhat consistent with slot velocity, it can beappreciated from FIG. 22, that the efficiency of Screen V-3 is inferiorto screens of the present invention.

TABLE 10 Screen Basket V-3 - Slot Width 0.16 mm/Profile Height 0.67 mmCleanliness Efficiencies (%) Slot Velocity Stickies Area Size Ranges(m/s) >0.04 mm² 0.04-0.3 mm² >0.3 mm² 1.53 79.1 63.3 96.0 1.52 80.0 47.198.0 1.52 74.0 52.1 93.9 1.53 75.9 56.4 98.0 1.45 82.3 58.9 96.9 1.4575.7 52.6 96.1 1.45 72.2 48.0 95.5 1.45 65.7 41.2 92.5 1.62 75.8 38.397.8 1.62 69.3 40.2 97.0 1.61 78.8 53.4 95.9 1.61 73.2 48.6 95.1 1.3875.5 46.0 97.3 1.39 72.2 41.6 97.1 1.39 73.2 49.3 96.1 1.39 70.3 40.097.2 1.44 75.2 46.0 98.8 1.43 81.3 52.6 99.0 1.44 74.8 47.0 98.5 1.4376.0 53.3 98.7 1.48 75.0 48.8 96.8

Example 6 (Comparative)

Table 11 presents the results obtained on another screen, A-1 not of theinvention, while those results are presented graphically in FIG. 23. Itcan be appreciated that the results are somewhat inconsistent with slotvelocity. It can also be appreciated from FIG. 23, that the efficiencyof Screen A-1 is quite low for this type of fiber.

TABLE 11 Screen Basket A-1 - Slot Width 0.11 mm/Profile Height 0.9 mmCleanliness Efficiencies (%) Slot Velocity Stickies Area Size Ranges(m/s) >0.04 mm² 0.04-0.3 mm² >0.3 mm² 1.16 80.4 46.1 97.3 1.15 77.6 39.096.8 1.18 63.8 29.1 82.9 1.19 62.2 32.0 87.1 1.20 78.7 37.2 96.4 1.2070.9 32.2 94.8 1.15 65.7 50.0 88.2 1.15 87.0 54.9 99.2 1.17 83.3 53.295.4 1.17 76.8 51.0 95.0 1.16 75.3 52.5 96.1 1.16 88.0 64.6 98.0 1.1584.6 61.1 98.7 1.22 80.6 45.6 97.1 1.15 84.2 63.3 98.2 1.15 65.9 41.385.2 1.18 83.0 62.4 93.9 1.18 87.1 53.7 99.1 1.28 73.8 38.2 95.4 1.2780.3 56.2 95.6 0.98 86.7 56.0 100.0 0.98 83.0 65.7 96.5 0.98 81.2 41.197.1 0.98 75.6 33.2 98.5 1.15 83.8 67.7 97.7 1.15 75.4 44.4 96.4 1.1784.3 63.9 98.7 1.18 81.3 42.7 99.4 1.17 74.9 38.8 98.8 1.18 66.5 38.195.4 1.15 67.9 27.4 92.9 1.16 65.7 20.0 95.4 1.21 64.3 29.0 93.1 1.2179.2 45.2 95.8 1.14 73.1 29.2 94.1 1.15 48.8 15.6 85.6 1.28 74.4 31.895.4 1.26 74.9 42.0 98.0 1.14 68.4 17.1 93.1 1.15 43.8 −32.1 77.4 1.2464.7 26.9 94.8 1.23 68.1 34.6 95.9 1.27 76.5 40.4 92.6 1.27 81.7 46.296.6 1.22 72.5 43.5 96.0 1.16 76.1 27.6 96.4 1.14 74.1 22.4 94.4 1.2883.0 51.6 97.1 1.28 65.9 27.0 88.6 1.26 73.8 45.5 91.1 1.15 76.2 35.192.4 1.16 55.6 3.4 81.7 1.17 74.4 40.1 94.4

The results of the preceding Examples 1-6 can be summarized in thefollowing set of Tables 12-17 which are graphically represented in FIG.24.

TABLE 12 Example 1 (Comparative) Averages from Table 6 Screen BasketV-5 - Slot Width 0.19 mm/Profile Height 0.62 mm Cleanliness Efficiencies(%) Slot Velocity Stickies Area Size Ranges (m/s) >0.04 mm² 0.04-0.3mm² >0.3 mm² 1.22 68.5 28.4 90.8

TABLE 13 Example 2 Averages from Table 7 Screen Basket V-4 - Slot Width0.14 mm/Profile Height 0.51 mm Cleanliness Efficiencies (%) SlotVelocity Stickies Area Size Ranges (m/s) >0.04 mm² 0.04-0.3 mm² >0.3 mm²1.72 84.6 67.3 97.7

TABLE 14 Example 3 Averages from Table 8 Screen Basket V-2 - Slot width0.13 mm/Profile Height 0.5 mm Cleanliness Efficiencies (%) Slot velocityStickies Area Size Ranges (m/s) >0.04 mm² 0.04-0.3 mm² >0.3 mm² 1.4085.1 59.4 97.4

TABLE 15 Example 4 (Comparative) Averages from Table 9 Screen BasketV-1 - Slot Width 0.11 mm/Profile Height 0.7 mm Cleanliness Efficiencies(%) Slot Velocity Stickies Area Size Ranges (m/s) >0.04 mm² 0.04-0.3mm² >0.3 mm² 1.38 81.6 50.1 96.3

TABLE 16 Example 5 (Comparative) Averages from Table 10 Screen BasketV-3 - Slot Width 0.16 mm/Profile Height 0.67 mm Cleanliness Efficiencies(%) Slot Velocity Stickies Area Size Ranges (m/s) >0.04 mm² 0.04-0.3mm² >0.3 mm² 1.48 75.0 48.8 96.8

TABLE 17 Example 6 (Comparative) Averages from Table 11 Screen BasketA-1 - Slot width 0.11 mm/Profile Height 0.9 mm Cleanliness Efficiencies(%) Slot velocity Stickies Area Size Ranges (m/s) >0.04 mm² 0.04-0.3mm² >0.3 mm² 1.17 74.4 40.1 94.4

It can be appreciated from Tables 12-17 and FIG. 24 that the cleanlinessefficiencies for stickies are quite sensitive to even small variationsin slot width and profile height.

While the invention has been described in connection with severalexamples, modifications to those examples within the spirit and scope ofthe invention will be readily apparent to those of skill in the art. Inview of the foregoing discussion, relevant knowledge in the art andreferences discussed above in connection with the Background andDetailed Description, the disclosures of which are all incorporatedherein by reference, further description is deemed unnecessary.

1. A method for screening recycled pulp comprising the steps of:fiberizing and suspending the pulp in an aqueous liquid; pressurizingsaid aqueous liquid; passing said aqueous liquid containing saidfiberized and suspended pulp to one screen having: a metallic screenbasket for screening of stickies having a supply side surfaceapproximating that of a right circular cylinder having an axis “A”, acircumference “C” and a diameter “D”, said surface comprising aplurality of sequences of facets, each sequence comprising a generallycircumferentially extending facet, an upstream generally diametrallyextending facet adjacent thereto, and a downstream generally diametrallyextending facet adjacent thereto, each said generally circumferentialfacet being generally parallel to the axis “A” of the cylinder andhaving a leading edge and a trailing edge, each said leading edge andtrailing edge as well as each said upstream generally diametrallyextending facet and each said downstream generally diametrally extendingfacet being generally parallel to the axis “A” of the cylinder, eachsaid leading edge being located upon a cylindrical surface S1, and eachsaid trailing edge being located upon a cylindrical surface S2, thediametral difference “δ” between the distance from the axis “A” to thecylindrical surface S1 and the diametral distance from the axis “A” tothe cylindrical surface S2 being between about 0.4 mm to about 0.6 mm,the normal direction to the surface of each said generallycircumferential facet in each sequence of facets having a componentdirected toward the adjacent trailing edge of an adjacent generallycircumferential facet in an adjacent sequence of facets , the angle “α”between the normal to each said generally circumferential facet and thediametral direction of said right circular cylinder being between about80° and 76°, the distance “t” from the leading edge to the trailing edgeof each said generally circumferential facet being between about 2.3 mmand 2.5 mm, the upstream generally diametrally extending facet of eachsequence adjoining the leading edge of a generally circumferential facetand the downstream generally diametrally extending facet of eachsequence adjoining the trailing edge, the distance “w” between theupstream generally diametrally extending facet of each sequence and thedownstream generally diametrally extending facet of the next adjacentsequence being between about 0.11 mm and 0.145 mm, a channel leadingfrom the supply side to the accepts side of said screen being definedbetween the upstream generally diametrally extending facet of eachsequence and the downstream generally diametrally extending facet of thenext adjacent sequence; a plurality of foils deployed adjacent saidsupply surface, each said foil being adapted to induce flow past saidaccepts surface of said screen basket and thereby periodically inducebackflow through said channels against the pressure applied to saidaqueous liquid, forward flow responsive to the pressure applied to saidaqueous liquid occurring during periods between said periodic backflow;conducting forward flow passing though said channels as an accepts flowto a papermaking operation; passing rejects flow from said supply sideof said screen basket to another screen; and recycling accepts from saidother screen back to the supply to said one stream.
 2. The method ofclaim 1, wherein the screen basket is comprised of a plurality ofmetallic faceted vanes.
 3. The method of claim 1, wherein the screenbasket is formed from at least one unitary metallic sheet, each sheethaving a plurality of trenches formed into its surfaces and a pluralityof slits formed therethrough.
 4. The method of claim 1 wherein thescreen basket comprises stainless steel.
 5. The method of any precedingclaim wherein a corrosion resistant hardened surface is disposed uponthe screen basket.
 6. The method of claim 1 wherein the screen basket isplated with chromium.
 7. The method of claim 6 wherein the screen basketbears a hard plating comprising a major proportion of chromium havinghardness of at least about 65 on the Rockwell C scale in a thickness ofat least 0.2 mils up to about 1.0 mils.
 8. A metallic screen basket forscreening of stickies containing recycled fibers, having a supply sidesurface approximating that of a right circular cylinder having an axis“A”, a circumference “C” and a diameter “D”, said surface comprising aplurality of sequences of facets, each sequence comprising a generallycircumferentially extending facet, an upstream generally diametrallyextending facet adjacent thereto, and a downstream generally diametrallyextending facet adjacent thereto, each said generally circumferentialfacet being generally parallel to the axis “A” of the cylinder andhaving a leading edge and a trailing edge, each said leading edge andtrailing edge as well as each said upstream generally diametrallyextending facet and each said downstream generally diametrally extendingfacet being generally parallel to the axis “A” of the cylinder, eachsaid leading edge being located upon a cylindrical surface S1, and eachsaid trailing edge being located upon a cylindrical surface S2, thediametral difference “d” between the distance from the axis “A” to thecylindrical surface S1 and the diametral distance from the axis “A” tothe cylindrical surface S2 being between about 0.35 mm to about 0.60 mm,the normal direction to the surface of each said generallycircumferential facet in each sequence of facets having a componentdirected toward the adjacent trailing edge of an adjacent generallycircumferential facet in an adjacent sequence of facets , the angle “a”between the normal to each said generally circumferential facet and thediametral direction of said right circular cylinder being between about80° and 76°, the distance “t” from the leading edge to the trailing edgeof each said generally circumferential facet being between about 2.30 mmand 2.5 mm, the upstream generally diametrally extending facet of eachsequence adjoining the leading edge of a generally circumferential facetand the downstream generally diametrally extending facet of eachsequence adjoining the trailing edge, the distance between the upstreamgenerally diametrally extending facet of each sequence and thedownstream generally diametrally extending facet of the next adjacentsequence being between about 0.11 mm and 0.145 mm, a channel leadingfrom the supply side to the accepts side of said screen being definedbetween the upstream generally diametrally extending facet of eachsequence and the downstream generally diametrally extending facet of thenext adjacent sequence.
 9. The metallic screen basket of claim 8,wherein the screen basket is comprised of a plurality of metallicfaceted vanes.
 10. The metallic screen basket of claim 8, wherein thescreen basket is formed from at least one unitary metallic sheet, eachsheet having a plurality of trenches formed into its surfaces and aplurality of slits formed therethrough.
 11. The metallic screen basketof any of claims 8 to 10 wherein the screen basket comprises stainlesssteel.
 12. The metallic screen basket of any of claims 8 to 10 wherein acorrosion resistant hardened surface is disposed upon the screen basket.13. The metallic screen basket of claim 8 wherein the screen basket isplated with chromium.
 14. The metallic screen basket of claim 13 whereinthe screen basket bears a hard plating comprising a major proportion ofchromium having hardness of at least about 65 on the Rockwell C scale ina thickness of at least 0.2 mils up to about 1.0 mils.
 15. An improvedscreen for separating a supply stream comprising an aqueous dispersionof papermaking fibers contaminated with adhesives into an accepts streamenriched in fibers and depleted in adhesive relative to said supplystream and a rejects stream enriched in adhesive and depleted in fiberrelative to said supply stream, said screen comprising: a housing; agenerally cylindrical screen basket disposed within said housing,defining an accepts region exterior to said screen basket; a supply ductissuing into said screen basket within said housing; an accepts ductleading from accepts region in said housing; and a rejects duct adaptedto receive aqueous dispersion not passing through said screen basket;wherein the improvement comprises; said screen basket comprising aplurality of metallic faceted vanes defining an interior supply sidesurface approximating that of a right circular cylinder having an axis“A”, a circumference “C” and a diameter “D”, each vane having formedtherein: a generally circumferentially extending facet, an upstreamgenerally diametrally extending facet adjacent thereto, and a downstreamgenerally diametrally extending facet adjacent thereto, each saidgenerally circumferential facet being generally parallel to the axis “A”of the cylinder and having a leading edge and a trailing edge, each saidleading edge and trailing edge as well as each said upstream generallydiametrally extending facet and each said downstream generallydiametrally extending facet being generally parallel to the axis “A” ofthe cylinder, each said leading edge being located upon an imaginarycylindrical surface S1 generally coaxial with said screen basket, andeach said trailing edge being located upon another imaginary cylindricalsurface S2 generally coaxial with said screen basket, the diametraldifference “d” between the distance from the axis “A” to the cylindricalsurface S1 and the diametral distance from the axis “A” to thecylindrical surface S2 being between about 0.35 mm to about 0.60 mm, thenormal direction to the surface of each said generally circumferentialfacet on each vane having a component directed toward the adjacenttrailing edge of an adjacent generally circumferential facet in anadjacent vane , the angle “a” between the normal to each said generallycircumferential facet and the diametral direction of said right circularcylinder being between about 80° and 76°, the distance “t” from theleading edge to the trailing edge of each said generally circumferentialfacet being between about 2.30 mm and 2.5 mm, the upstream generallydiametrally extending facet of each vane adjoining the leading edge of agenerally circumferential facet and the downstream generally diametrallyextending facet of each vane adjoining the trailing edge, the distancebetween the upstream generally diametrally extending facet of each vaneand the downstream generally diametrally extending facet of the nextadjacent vane being between about 0.11 mm and 0.145 mm, a relievedchannel leading from the supply side to the accepts side of said screenbeing defined between the upstream generally diametrally extending facetof each vane and the downstream generally diametrally extending facet ofthe next adjacent vane.
 16. The improved screen of claim 15, wherein thescreen is comprised of a plurality of metallic faceted vanes.
 17. Theimproved screen of claim 15, wherein the screen is formed from at leastone unitary metallic sheet, each sheet having a plurality of trenchesformed into its surfaces and a plurality of slits formed therethrough.18. The improved screen of any of claims 15 to 17 wherein the screencomprises stainless steel.
 19. The improved screen of any of claims 15to 17 wherein a corrosion resistant hardened surface is disposed uponthe screen.
 20. The improved screen of any of claims 15 to 17 whereinthe screen is plated with chromium.
 21. The improved screen of claim 15wherein the screen bears a hard plating comprising a major proportion ofchromium having hardness of at least about 65 on the Rockwell C scale ina thickness of at least 0.2 mils up to about 1.0 mils.